Operations, such as geophysical surveying, drilling, logging, well completion and production, are typically performed to locate and gather valuable downhole fluids. Surveys are often performed using acquisition methodologies, such as seismic mapping, resistivity mapping, etc. to generate images of underground formations. These formations are often analyzed to determine the presence of subterranean assets, such as valuable fluids or minerals, or to determine if the formations have characteristics suitable for storing fluids. Although the subterranean assets are not limited to hydrocarbons such as oil, throughout this document, the terms “oilfield” and “oilfield operation” may be used interchangeably with the terms “field” and “field operation” to refer to a site where any types of valuable fluids or minerals can be found and the activities required to extract them. The terms may also refer to sites where substances are deposited or stored by injecting them into the surface using boreholes and the operations associated with this process. Further, the term “wellbore operation” refers to a field operation associated with a wellbore, including activities related to wellbore planning, wellbore drilling, wellbore completion, and/or production using the wellbore.
Fractures in the earth play an essential role in influencing the movement of fluids in rocks. Fractures may be of natural origin or may be created artificially by operations associated with the exploitation of hydrocarbon or mineral reserves. For example, fractures may be deliberately induced in an oil or gas well by raising the wellbore fluid pressure until the surrounding rock fails in tension. Such rock failure may include failures in shear, pore collapse, etc. Fractures produced in this manner are known as hydraulic fractures and they are frequently used in the petroleum industry to enhance production (i.e., stimulation) by providing high permeability conduits that promote the flow of hydrocarbons into the wellbore.
The production of hydrocarbon and the stimulation design is historically based upon intrinsic properties of the rock such as petrophysical properties or stiffness properties and extrinsic loading of the formation such as the magnitude and orientation of the far-field stress. Typically these formation parameters are used to affect the operation of the wellbore drilling and completion procedure. For example porosity, saturation, permeability, natural fractures, stress magnitude and orientations have been measured to characterize the reservoir. However, the application of these properties has not fully solved the dilemmas encountered in hydraulic stimulation and drilling optimization. The production and drilling profile in many wellbores are highly variable. It has been observed in numerous vertical and horizontal completions to have non uniform production, to the point that many intervals are not flowing. The pressures measured in the wellbore during hydraulic fracturing may be interpreted to obtain an estimate of the magnitude of stress in the earth. In order to optimize production and understand where fractures may be induced in the formation, it is essential to correctly interpret stress in the earth based on an understanding of local geology and how it relates to the local reservoir properties.